1. Field of the Invention
The present invention relates generally to transmitting very low-level signals to through a set of electrical contacts and, more particularly, to utilizing a two-wire signal transmitter circuit to add a very low-level alternating current (AC) signal to a low-level Direct Current (DC) bias that is of sufficient level to overcome minimum ratings of poor electrical contacts, and further, with the use of a unity gain current amplifier, to reduce the signal degrading effects of long signal paths.
2. Description of the Related Art
As is well known in the art, electrical contacts that degrade over long time periods are sometimes utilized, for functional and economic reasons, to control applications such as train control and protection. These poor electrical contacts present a challenge to the application engineer who must transmit very low level but critical sensor signals through such contacts. In particular, in the case of Automatic Train Coupler contacts that are used for connecting circuits that run the length of a train, signal degradation often may be caused by: poor contacts that require higher minimum contact ratings; a plurality of contacts through which the signal must pass; degradation of the contacts themselves; and the significant lengths of wire that often interconnect the contacts. The poor contacts mentioned are of the type that have minimum contact ratings typically requiring the signals that pass through them to have amplitude levels of at least twelve (12) volts and current levels of at least 0.01 amperes. However, some sensor signals that have levels measuring approximately 1/1000 of each of those minimum contact ratings must be passed through the poor electrical contacts.
Consequently, particular to train control and similar applications, a need has been felt for providing an improved signal transmitter and method which overcomes the signal degrading effects of poor contacts and very long signal transmission paths that may be associated with those poor contacts.